Poster: Oxidative Stress

Abs # 113: Effects of abiotic stresses on the photosynthesis of mangrove leaves

Presenter:	Takabe, Tomoko , tomokociviclev@sage.ocn.ne.jp
Authors	Takabe, Tomoko  (A)   Tanaka, Yoshito  (B)   Hibino, Takashi  (B)   Takabe, Teruhiro  (B)
Affiliations:	(A): Nagoya University (B): Meijo University

Mangroves are woody plants which form the dominant variation in tidal, saline wetlands along tropical and subtropical coasts. High light and high salinity of intertidal mangrove habits impose at least two potential restrictions on the photosynthetic rate of mangrove leaves; high water deficiency and low stomatal conductance, both would inevitably result in a larger excess of excitation energy. Excess excitation energy is injurious to the photosynthetic systems. Overreduction of the photosynthetic electron transport chain causes the generation of active oxygen species such as singlet oxygen, superoxide anion, hydrogen peroxide, and hydroxyl radical. Therefore, the enhancement of enzyme activity involved in active oxygen scavenging systems may be a potent strategy to increase salt tolerance in mangrove. An alternative strategy to cope with oxidative damage might be the suppression of active oxygen production through photorespiration. Photorespiration may function as a possible route for the dissipation of excess light energy or reducing power. Photorespiration is a metabolic pathway in which CO₂ is released by light and is linked to Calvin-Benson cycle through the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The main objective of the present study was to investigate how mangrove leaves respond to excess light under abiotic stresses. Changes in chlorophyll fluorescence and gas exchange of Avicennia marina were simultaneously examined under various stress conditions. From these measurements, we estimate the velocity of carboxygenase reaction (Vc) and oxygenase reaction (Vo) of Rubisco as well as the electron flow producing active oxygen. The data suggested the importance of oxygenase reaction of Rubisco.